1. Field of the Invention
The present invention relates to a technique of displaying images on a screen using a liquid crystal panel and other display elements, for example, a liquid crystal projector, a reflection type image displaying projector, a liquid crystal television and a projection type display apparatus.
A projection type imaging apparatus such as a liquid crystal projector has been popular, in which the display element such as a liquid crystal panel or the like is irradiated with a light beam emitted from a light source and thereby an image on the display element can be projected as an enlarged image.
In the imaging apparatus of this type, the light from the light source is adjusted through conversion to gray scale of each pixel with the display element and is then projected to the screen. For example, in the case of the twisted nematic (TN) type liquid crystal display element in which the display element is a typical example of the liquid crystal display element, two sheets of polarizing plates are arranged to result in a difference of 90 degrees of polarizing directions before and after the liquid crystal cell which is formed by supplying the liquid crystal to the space between a couple of transparent substrates having the transparent electrode films. In this case, amount of transmitting light of the incident light beam is controlled to display the image of information by combining the operations for rotating the polarizing plane with the electro-optical effect of the liquid crystal and selecting the polarizing element of the polarizing plate. In recent years, such transmitting type or reflection type display element has remarkably reduced the size of the element itself and also has improved performance such as resolution, etc.
Therefore, with advancement in size reduction and performance of the apparatus utilizing the display element, a projection type imaging apparatus has newly been proposed as an apparatus not only for realizing image formation by a video signal or the like which has been done in the related art, but also for use as an image output device of a personal computer. The projection type imaging apparatus of this type is particularly required to be small in size and to assure that a bright image can be obtained up to the corners of the display screen.
However, the projection type imaging apparatus of the related art has problems that the apparatus size is large and brightness and quality of image attained finally are insufficient.
For example, in the case of a liquid crystal display apparatus, size reduction of the light bulb, namely liquid crystal element itself is effective for size reduction of the apparatus as a whole, but when the liquid crystal display element is reduced in size, the area irradiated by the light of liquid crystal means becomes small, creating a problem in that a ratio in amount of light flux on the liquid crystal display element for amount of total light flux radiated by the light source (hereinafter, referred to as light application efficiency) becomes lower and side area of display screen becomes dark. Moreover, since the liquid crystal display element can utilize the polarized light beam of only one direction, about a half of the light beam emitted from the light source which radiates the random polarized light beam is left unused.
As a means for attaining the bright image at the four sides of the display screen, an integrator optical system, for example, has been proposed, in which a couple of lenses are used as described in the Japanese Published Unexamined Patent Publication No. HEI 3-111806. The integrator optical system divides the light from the light source with a plurality of condenser lenses in the shape of the rectangular opening forming a first array lens and then focuses in overlapping the output light in the shape of rectangular opening at the radiating surface (liquid crystal display element) with a second array lens formed by the condenser leans group corresponding to the condenser lenses in the shape of rectangular opening. In this optical system, intensity distribution of the light irradiating a the liquid crystal display element can be almost equalized. Meanwhile, as the optical system for irradiating the liquid crystal display element with the light beam emitted from the light source and arranged in one polarizing direction, a system is disclosed in the Japanese Published Unexamined Patent Publication No. HEI 4-63318, in which the light beam emitted from the light source and is polarized at random is isolated to P-polarized light beam and S-polarized light beam using the polarizing beam splitter and these are then combined with a prism.
However, in the conventional integrator optical system, since a diagonal size of one lens cell of array lens is 0.25 inch or larger, an F value of the light system must be set to almost 2 or 3 in order to improve equality of brightness and quality of image using the liquid crystal display element with a micro-lens. As a result, distance between the first and second array lenses becomes not shorter than 31 mm, disabling reduction in size of the optical system. Therefore, it has been difficult for the projection type liquid crystal apparatus of the related art to reduce the size of apparatus exceeding the size of the A4 file size. Moreover, even in the optical system utilizing the polarizing beam splitter, it is difficult to realize matching in accuracy in the array lens and therefore size reduction has also been difficult. As a result, it has been difficult to simultaneously realize reduction in size of the apparatus as a whole and improvement in performance such as brightness. In addition, in the case of the projection type liquid crystal apparatus, it has also been difficult, even when only the lighting means is improved, to attain the display apparatus which is small in size and assures good display image quality because the image quality depends on various factors, in addition to such lighting means, such as optical characteristic of objection leans and optical characteristic of liquid crystal element.
Moreover, it has been required to use a larger array lens in order to improve brightness in the integrator optical system of the related art and when the projection type liquid crystal apparatus is reduced in size, brightness has been decreased. In addition, this phenomenon can also be observed when size reduction is conducted in the optical system using the polarizing beam splitter. As a result, it has been difficult to simultaneously realize size reduction of the apparatus as a whole and improvement in performance such as brightness. Moreover, when a polarized beam combining means is used, performance deterioration due to unwanted light beam, namely the P-polarized light beam entering the S light path has also been observed.